Search Results (327)

Surface roughening is a common defect in plastic deformation processing, directly affecting product surface quality and service performance. This study investigates the mechanisms of surface roughness evolution during plastic deformation by considering both intrinsic and extrinsic factors. A macro–meso-scale modelling framework is developed by coupling crystal plasticity finite element modelling, fluid–solid interaction modelling, and macro–meso boundary conditions. The crystal plasticity model incorporates a constitutive model based on crystal plasticity theory, a Voronoi-based geometric model, and a real rough-surface topography model to capture non-uniform grain-scale plastic deformation. Fluid–solid interaction modelling is introduced to analyze the influence of liquid lubricant on the deforming solid material. Boundary interpolation and continuous displacement theories are then used to transfer macro-scale boundary constraints to the meso scale. The proposed framework is numerically implemented and applied to the aluminum alloy tube drawing process. The effects of intrinsic factors, including grain size, grain orientation, and initial surface roughness, and extrinsic factors, including deformation path, strain rate, and lubrication condition, are systematically examined. From a practical point of view, effective strategies to improve surface quality are by reducing grain size, lowering initial surface roughness, decreasing the strain rate and using low-viscosity lubricants. Full article

Granular collapse-induced wave generation is a critical process in coastal engineering and natural hazards, yet its rapid and complex fluid–solid coupling mechanism poses significant challenges for numerical modeling. This paper presents a comprehensive validations and performance benchmarking study of non-spherical granular collapse-induced wave generation using a GPU-accelerated resolved SPH-DEM coupling framework. Through three benchmark cases with increasing complexity, the numerical accuracy and robustness of the model are thoroughly verified with respect to free-surface flows, multi-body collisions, and intense fluid–solid interactions. Subsequently, the influence of SPH resolution and particle shape on computational efficiency is quantitatively assessed. It is found that the total runtime is dominated by the number of SPH particles, while the GPU acceleration advantage becomes more pronounced as the number of DEM faces increases. Furthermore, in the granular collapse-induced wave case, the temporal evolution of the leading wave amplitude and the difference in granular runout distance under dry and wet conditions are analyzed, revealing from the particle scale how fluid resistance modulates the coupling between wave generation and granular motion. This study not only validates the capability of the model to capture complex particle–wave interactions, but also provides quantifiable performance benchmarks and physical insights for its engineering applications. Full article

Thermal runaway of lithium-ion batteries involves rapid heat release, gas generation, and multiphase transport, but their interaction inside a cell remains difficult to resolve. A multiscale computational fluid dynamics model was developed for a single 18650 cell by coupling microscale reaction kinetics, mesoscale interfacial heat transfer, and macroscale gas–liquid transport with a stationary porous-solid energy balance. The model describes internal temperature and the evolution of carbon dioxide, oxygen, water vapour, and hydrogen fluoride while examining the effects of porosity and the modelled dimethyl carbonate mass fraction. The medium-to-fine grid difference in carbon dioxide mass fraction was approximately 0.16%. Time steps of 0.01, 0.001, and 0.0001 s produced mass fractions of 0.0564, 0.0617, and 0.0618, respectively. Increasing the solvent mass fraction and porosity primarily shortened the induction period, while the peak temperature and terminal species levels remained similar. A quadratic response surface fitted to the simulation database was searched using grey wolf, genetic, and particle swarm methods. Grey wolf and particle swarm gave candidate times to peak temperature of about 238.8 s, whereas the genetic method gave 237.2 s, a difference of 1.6 s (0.67%). Particle swarm reached the high-response region within fewer iterations, while grey wolf maintained broader exploration. The proposed model connects reaction kinetics with macroscopic temperature and species evolution and clarifies how electrolyte composition and porous structure regulate the time scale of thermal runaway. Full article

Background: Lipid nanoparticles are widely investigated as oral drug delivery systems, but their intestinal performance remains difficult to predict based only on physicochemical properties. This study aimed to elucidate how the lipid matrix composition influences the intestinal permeation of curcumin from lipid nanoparticles. Methods: Curcumin-loaded nanoemulsions, nanostructured lipid carriers with defined solid-to-liquid lipid ratios, and solid lipid nanoparticles were prepared by high-pressure homogenization. All formulations were characterized with respect to particle size, polydispersity index, and zeta potential before and after simulated intestinal pre-incubation in a simplified SDS-containing intestinal fluid. Intestinal permeation was evaluated ex vivo using porcine gut tissue by analysis of semi-quantitative fluorescence-based permeation readouts (ART) and mean permeation depth (MPD) after 30 and 60 min. Results: All formulations maintained stable physicochemical properties with particle sizes around 200 nm and negative zeta potentials; pre-incubation increased the negativity of the zeta potential but left particle size unchanged. Despite similar attributes, the formulations differed in intestinal curcumin permeation based on time and composition. At 30 min, nanoemulsions and mixed nanostructured lipid carriers achieved the highest performance. By 60 min, lipid carriers with more liquid lipid significantly increased both the fluorescence intensity and the depth of curcumin permeation, while other systems showed little further improvement. Conclusions: The intestinal permeation of drug from lipid nanoparticles is governed by the lipid matrix architecture and its interaction with the hydrated intestinal environment, which together affect drug-release kinetics and the ability to sustain a trans-epithelial concentration gradient over time. Thus, optimizing oral lipid nanoparticles requires time-resolved, biologically relevant models rather than physicochemical characterization alone, consistent with observed similar matrix-driven effects in dermal delivery systems. Full article

Natural-fracture connectivity substantially influences hydraulic-fracture interaction with pre-existing discontinuities, but its quantitative role in fracture-network propagation remains insufficiently constrained. In this study, a coupled LEFM–cohesive-zone hydraulic-fracture propagation model was developed by combining crack-tip deflection criteria, traction-separation damage evolution and fluid–solid coupling. True triaxial hydraulic-fracturing experiments were conducted on artificial fracture networks with I-, V-, Y- and X-shaped connectivity elements to evaluate the model response. The results show that connected natural fractures redirect hydraulic fractures under low horizontal stress differences, producing deflection angles of 30–50 degrees. When the stress difference exceeds 4 MPa, fracture growth becomes more strongly aligned with the maximum principal stress direction. In the true triaxial tests, the total number of connected natural fractures increased from 14 in the I-shaped network to 17 and 21 in the Y- and X-shaped networks, corresponding to increases of 21.4% and 50.0%, respectively. X-shaped networks showed the strongest sensitivity to stress difference and injection rate, while higher elastic modulus reduced fracture width and promoted longer, narrower fractures. Scale-normalized comparisons based on image-derived experimental measurements showed that the predicted propagation length, fracture width and connected-fracture number followed the experimental trend from I-shaped to Y-shaped and X-shaped networks, with relative errors within 7.1% and a mean absolute percentage error of 4.8%. These findings suggest that fracture topology strongly influences pressure transmission and multidirectional activation in the tested models, whereas field-scale extrapolation requires three-dimensional validation and transport analysis. Full article

Building on previous work to understand mental transformation of solid objects, our work aims to contribute to theory on how individuals visualize fluid transformation. Working at the intersection of discipline-based research in fluid-Earth sciences (oceanography and atmospheric science) and cognitive science, we began by characterizing students’ mental models of fluids in solid body rotation. Using a common pedagogical tool of oceanography and atmospheric science instructors—large water filled rotating tanks—we conducted semi-structured, interactive interviews in conjunction with demonstrations of solid body fluid rotation to elicit participants’ sketched predictions and explanations of their reasoning. We used emergent coding to analyze the data and found that participants confidently predicted fluid behavior; however, their predictions were highly inaccurate, much to the participants’ surprise. These results suggest that the behavior of rotating fluids is unintuitive, and that the mind adopts prior experiences with fluids to fill the gap. We suggest that a better understanding of how humans reason about fluids can inform the cognitive science of event processing and suggest that framing mental transformation using an event perspective may be a productive approach. Full article

The present work introduces a fully resolved three-dimensional thermal Lattice Boltzmann framework developed to investigate the impact of freely moving, finite-size spherical particles on natural convection within a cubic enclosure. The fluid-phase momentum and energy fields are resolved using coupled double-distribution function kinetic approach, while the solid phase is governed by explicitly coupled linear, angular, and thermal conservation equations. To accurately map the moving spherical surfaces onto the Eulerian lattice grid, a second-order linear interpolated bounce-back scheme is implemented. The conjugate heat transfer between the phases is simplified via a lumped capacitance model, assuming negligible internal thermal resistance within the solid spheres. Short-range particle–particle and particle–wall interactions are handled using Glowinski’s repulsive force model. The spatial accuracy of the framework is validated using a circular Taylor–Couette flow benchmark—demonstrating second-order spatial convergence and a differentially heated natural convection in a cubic cavity benchmark, yielding bulk Nusselt numbers within $1\%$ of established literature data. This validated tool is subsequently used to analyze the complex interplay between particulate motion and bulk thermal transport efficiency. Analysis of the temperature fields reveals that the overall thermal structure is governed primarily by the Rayleigh number, while the low particle concentration produces only minor modifications to the convective heat transfer. In contrast, the particle distribution exhibits a strong dependence on the flow intensity. Full article

Understanding pore-scale interactions among CO₂, the aqueous phase, and heavy oil is crucial for optimizing surfactant-assisted CO₂-enhanced oil recovery. In this study, a three-phase volume-of-fluid (VOF) framework is established in OpenFOAM to simulate immiscible displacement in two-dimensional porous media composed of circular solid grains. Two pore geometries are considered: a relatively uniform geometry and a preferential-channel geometry designed to promote early breakthrough. Sixteen injection schemes are compared, including pure CO₂ flooding, ordinary-water flooding, surfactant–water flooding, aqueous-phase preflush followed by CO₂ injection, and cyclic aqueous-phase/CO₂ injection with different aqueous-slug durations and switching frequencies. The effects of pore geometry, injection strategy, capillary number, viscosity ratio, interfacial tension, and wettability are evaluated using pore-volume-normalized oil recovery, breakthrough PV (the ratio of injected volume to pore volume), cumulative injected CO₂ PV at breakthrough, and phase-distribution indicators. The results show that pore geometry strongly affects macroscopic sweep and breakthrough behavior. In the preferential-channel geometry, pure CO₂ flooding and continuous ordinary-water flooding suffer from early breakthrough and poor sweep, whereas continuous surfactant–water flooding maintains high recovery because reduced oil–water interfacial tension and a more water-wet wall condition promote oil-film detachment and residual-oil mobilization. At 2.5 injected PV, the high-frequency short-slug and 1 s surfactant–water cyclic schemes give the highest or near-highest recovery in the relatively uniform geometry, while continuous surfactant–water flooding remains the highest-recovery scheme in the preferential-channel geometry. Considering the higher chemical demand of continuous surfactant injection and the carbon-utilization objective of CO₂-EOR, the combined surfactant–water/CO₂ schemes are evaluated to clarify the coupling between surfactant-induced oil mobilization and CO₂ displacement. Surfactant–water preflush followed by CO₂ injection becomes more effective as the preflush duration increases, and its recovery advantage over ordinary-water preflush is especially large in the preferential-channel geometry. However, the increase in CO₂ breakthrough PV in this geometry is limited compared with the recovery increment, indicating that the main benefit of surfactant–water is not only delayed gas breakthrough but also enhanced microscopic oil mobilization in poorly swept regions. Increasing the switching frequency slightly improves the cyclic response in the relatively uniform geometry under the tested schedules, whereas all cyclic schemes remain strongly constrained by reconnection with the dominant gas pathway in the preferential-channel geometry. Within the present idealized immiscible VOF model, these comparisons provide a controlled pore-scale comparison for distinguishing surfactant-induced residual-oil mobilization from CO₂ gas-channeling effects in heavy-oil porous media. Full article

Currently, Computational Solid Mechanics (CSM) and Computational Fluid Dynamics (CFD) simulations are not enough to correctly estimate the different physical characteristics found in the human cardiovascular system. As an alternative to individual simulations, Fluid Structure Interaction (FSI) simulations can yield more accurate physical quantities. In this study a comparison between rigid-wall CFD of a thoracic aorta affected by an aneurysm and the FSI of the Descending Thoracic Aortic Aneurysm (DTAA) itself was performed. The 18-year-old patient-specific geometry of the aorta and its branches was based on the National Institutes of Health public database. A patient-specific pulsatile blood flow waveform and a pressure three-element Windkessel model were set for boundary conditions. Parameters such as wall pressure, velocity distribution, Wall Shear Stress (WSS), Time-averaged Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), wall displacement and Von Mises Stress (VMS) were investigated. The research shown that blood flow in the aorta is strongly affected by the onset of the aneurysm, which causes recirculation and uneven flow within the aneurysmal bulge. The results highlight that rigid-wall CFD, which cannot capture wall deformation and aneurysm compliance, leads to an overestimation of velocity, WSS, and TAWSS by 15, 21, and $32\%$ respectively, compared to FSI during the systolic peak; furthermore, a key novelty is represented by the slight underestimation of pressure during the systolic peak, an aspect not previously detailed in the DTAA literature. Full article

As a sustainable alternative to fossil fuels, geothermal energy plays a critical role in the global shift toward carbon neutrality. However, the economic extraction of heat is frequently hindered by poor-reservoir permeability, often exacerbated by mineral scaling and particulate clogging during long-term operation. This review provides a comprehensive synthesis of acidization technologies, emphasizing their mechanisms for enhancing injectivity and productivity in diverse geothermal settings. This study scrutinizes the chemical interaction between varied acid systems ranging from conventional mineral acids to solid organic acid blends and the complex geological conditions of volcanic and sedimentary reservoirs. Furthermore, the paper delineates the evolution of geothermal energy development methods, such as matrix acidizing and hydraulic fracturing synergy (multi-stage acid fracturing), alongside metal corrosion inhibition and effluent scale treatment. By integrating empirical field data with theoretical geochemical modeling, this review provides an in-depth analysis of the acid fracturing mechanisms within coupled thermal–hydraulic–mechanical–chemical (THMC) fields. It further identifies the persistent challenges of high-temperature stability and deep-seated flow path diversion. Ultimately, this paper proposes a roadmap for next-generation “smart” acidizing fluids, aiming to provide a robust framework for optimizing geothermal heat mining and ensuring the longevity of enhanced geothermal systems. Full article

Rock-bed thermal energy storage (RTES) systems are attracting growing interest as low-cost, robust, and scalable sensible heat storage solutions for applications ranging from low-temperature building and greenhouse heating to medium- and high-temperature solar or waste-heat recovery systems. However, their thermo-hydraulic performance is strongly influenced by the complex interactions among heat-transfer-fluid flow, irregular rock morphology, porosity, pressure drop, interphase heat transfer, and transient thermal-front development. This review provides a focused evaluation of computational fluid dynamics (CFD) modelling strategies for packed beds of rocks, with particular attention to continuum porous-medium approaches and the closure correlations required for reliable simulation. First, the distinction between pore-scale and volume-averaged continuum modelling is discussed in terms of the trade-off between physical resolution and computational feasibility. The main pressure-drop and friction-factor correlations are then reviewed and compared, including classical packed-bed models and rock-bed-specific formulations. It is shown that hydraulic-resistance predictions are highly sensitive to particle shape, surface roughness, porosity, the bed-to-particle diameter ratio, and packing arrangement. Particle-fluid heat-transfer correlations are also examined and, when possible, converted into a consistent particle Nusselt-number form to enable direct comparison. Particular attention is given to generalized correlations, dispersion-corrected models, and air–rock-bed correlations applicable to thermal storage systems. Finally, a methodological framework for modelling RTES systems using local thermal equilibrium (LTE) and local thermal non-equilibrium (LTNE) formulations is proposed. Dimensionless criteria, including the interphase thermal coupling number and particle Biot number, are introduced to support the selection between LTE and LTNE formulations. The selection of pressure-drop/friction-factor and solid–fluid heat-transfer/particle Nusselt-number correlations should be based on the similarity between the original experimental conditions and the target RTES system, and system-specific validation is recommended whenever possible. Full article

Background/Objectives: α-lipoic acid (ALA) shows therapeutic potential but faces poor aqueous solubility (BCS Class II), gastric instability, and low oral bioavailability (~30%). This work investigated the formulation of cyclodextrin (CD) inclusion complexes of ALA to overcome the aforementioned limitations and improve nutraceutical applications. Methods: Phase solubility studies in simulated gastric and intestinal fluids screened for optimal CD, followed by molecular dynamics simulations and MM-PBSA binding free energy calculations. Inclusion complexes of choice were prepared by grinding, spray-drying, and lyophilization, followed by solid-state characterization (DSC/XRPD/FTIR). Further analysis was performed using pH-shift dissolution (USP II), permeability (PermeaPad^®, Caco-2), and (photo)stability according to ICH. Results: Hydroxypropyl-β-cyclodextrin (HPβCD) emerged as the optimal host due to favorable complexation, as confirmed by phase solubility studies and supported by molecular modeling, which revealed a favorable balance between inclusion complex stability and pH-triggered drug release. Formulations based on spray-dried and lyophilized HPβCD–ALA complexes (HPβALA-sd and HPβALA-lyo), in which ALA was fully amorphized, achieved near-complete dissolution within five minutes under biorelevant pH-shift conditions. This performance markedly exceeded that of free ALA (approximately 66% dissolution at pH 7.4) while maintaining moderate permeability (Papp 8–9 × 10⁻⁶ cm/s). Storage stability was enhanced markedly (88–90% ALA retention after 6 months at 40 °C/75% RH vs. 36% for free ALA) while UV stability was not improved through CD-complexation, probably due to interaction of UV-VIS light with the exposed portion of ALA. Conclusions: Even though the permeability of ALA–CD inclusion complexes remained medium (Papp ~ 8–9 × 10⁻⁶ cm/s) and unaffected by complexation, a significantly improved dissolution profile indicates better expected bioavailability compared to pure ALA. Full article

Gas–solid bubbling fluidized beds involving Geldart Group B particles are fundamental to numerous industrial thermochemical processes, where bubble dynamics dictate the efficiency of heat and mass transfer. However, accurately predicting these complex hydrodynamic behaviors remains a challenge due to the non-linear coupling of phase interactions. This study presents a comprehensive validation of 2D and 3D Eulerian–Eulerian Two-Fluid Models (TFM) against an extensive experimental dataset. A ‘core-flow’ consistency principle is adopted, demonstrating that the 3D cylindrical simulation provides a physically equivalent representation of the central bubbling dynamics in the rectangular experimental bed. A key innovation of this work is a novel post-processing framework that bridges raw CFD datasets and quantitative bubbling metrics. Unlike traditional threshold-based segmentation or localized probe measurements, which are often limited by spatial resolution and noise sensitivity, the integrated use of Autodesk 3DS Max for volumetric reconstruction and customized MATLAB (R2024a) algorithms allows for the seamless processing of heterogeneous 2D and 3D data. This methodology significantly enhances the capability to track complex bubble coalescence and breakup events while improving batch-processing efficiency, providing a high-fidelity alternative for analyzing gas–-solid flow patterns in complex geometries. The results show that both experimental data and 2D simulations align with Werther’s correlation, yielding Mean Relative Errors (MRE) of 8.2% and 10.5%, respectively. In contrast, the 3D simulation tracks Darton’s prediction closely with a lower MRE of 7.4%, demonstrating superior concordance in volumetric bubble growth. The core innovation lies in the definition of a clear dimensional choice framework: 2D simulations are computationally sufficient and accurate for predicting macro-scale bubble heights and frequencies under pseudo-2D or narrow-bed constraints. However, 3D simulations are strictly necessary when evaluating unconstrained radial expansion, core-flow dynamics, and precise volumetric bubble diameters (d_v) where full multi-directional degrees of freedom dictate hydrodynamics. Full article

Deep unconventional oil and gas reservoirs are critical to hydrocarbon exploration and development in China. However, their complex geological and petrophysical features, including high temperature, high pressure, high salinity, multiple pressure systems, and intricate pore–fracture structures, make them highly susceptible to formation damage during drilling, completion, stimulation, and production. Effective reservoir protection is therefore essential for minimizing damage and improving development efficiency. This paper systematically reviews recent advances in reservoir protection for deep unconventional reservoirs, with a focus on evaluation methods and protective materials. Laboratory evaluation methods, including permeability recovery, nuclear magnetic resonance, pressure decay, and spontaneous imbibition, together with field-based approaches such as well testing and production decline analysis, are summarized and assessed for their applicability to complex damage characterization. Major damage mechanisms, including liquid-phase trapping, solid invasion, sensitivity damage, stress sensitivity, and wettability alteration, are analyzed with emphasis on working fluid–reservoir interactions under multi-field coupling conditions. Recent progress in protective materials is also reviewed, covering polymer-based materials such as gel sealing agents, delayed-swelling hydrogels, water-/oil-soluble temporary plugging agents, and film-forming polymers, as well as ultrafine CaCO₃ and fiber-based materials. In addition, related protection technologies, including temporary plugging, film-forming fluid-loss control, underbalanced drilling, and low-damage completion fluids, are discussed. Existing models developed for conventional sandstone reservoirs are insufficient for deep unconventional systems. Future research should prioritize integrated evaluation and protection methods tailored to deep tight, shale, and fractured–vuggy carbonate reservoirs. This review provides a basis for understanding complex damage mechanisms, developing functional protective materials, and advancing integrated reservoir protection technologies for the efficient development of deep unconventional resources. Full article

This study presents a computational and experimental aerodynamic characterisation of a full-scale 5.5 m diameter, six-sail horizontal-axis windmill of the traditional Cretan Lasithi type, equipped with flexible woven polyester sails that act as a passive load-control mechanism. Seventeen operating points spanning wind speeds of 2.3–18.3 m/s were simulated in OpenFOAM using a transient sliding-mesh Arbitrary Mesh Interface formulation with the k–ω SST turbulence closure on a 2.3 million cell grid, selected on the basis of a four-level grid convergence study. CFD simulations identify three distinct aerodynamic regimes: a drag-dominated high-TSR regime (λ > 2.1), a mixed lift–drag working range with peak loading near λ ≈ 1.4–1.5, and a deep-stall regime in which boundary-layer separation propagates from root to tip as λ falls below 1.0. Field measurements conducted at the Energy Systems Synthesis Lab of the Hellenic Mediterranean University in compliance with IEC 61400-12-1:2005(E) confirm that rotor speed stabilises passively at 55–58 RPM above 13 m/s without any active control mechanism; CFD predictions agree with measured power output within 8–12% across the 2–13 m/s attached-flow envelope. The combined evidence indicates that passive overspeed self-regulation is driven by aeroelastic sail deformation, reducing effective disc solidity at high wind speeds, a mechanism that rigid-geometry CFD correctly identifies in trend but cannot quantify in magnitude. The primary limitation of the present work is the rigid-sail assumption of the CFD model, which requires a two-way coupled fluid–structure interaction extension as a future step. Full article